1. Field of the Invention
The present invention relates to a method for measuring a concentration of a biogenic substance and a measuring apparatus used for the method, particularly a method for measuring a concentration of a biogenic substance such as glucose contained in a living body, and a measuring apparatus used for the method.
2. Description of the Related Art
A concentration of a biogenic substance such as glucose contained in a living body is measured based on reflected light, scattered light or transmitted light of light radiated on the living body. More specifically, Raman scattering of the biogenic substance is observed, and the concentration of the biogenic substance is calculated based on the intensity of the Raman scattering.
Conventionally, Raman spectroscopy has been used in various applications and, for example, there is a disclosed technique for measuring a concentration of a biogenic substance by using Raman spectroscopy (for example, see JP 9-079982 A). The use of Raman spectroscopy can eliminate the need for consumables such as reagents, test strips, and enzymes in order to determine the concentration of a characteristic substance in biogenic substances; further eliminate the problem of preservation stability of the consumables before use, the problem of disposal of the consumables after use, and the problems of cumbersome operations contributing to errors and interferences from other substances; and moreover quantitatively measure multiple substances at once.
As a method of surface enhanced Raman spectroscopy, there is a disclosed technique which allows a surface enhanced Raman scattering substrate made of a group of noble metal colloids to coexist with a Raman active substance having stoichiometric relation with a substance to be analyzed, and measuring surface enhanced Raman scattering due to its enhanced electric field (for example, see JP 2004-205435 A). According to this technique, surface enhanced Raman scattering can be excited efficiently by light with a wavelength in the near-infrared region. By exciting surface enhanced Raman scattering with light in the near-infrared region and performing analysis by Raman spectroscopy in the near-infrared region, it is possible to eliminate effects of light absorption and fluorescence of foreign substances in a matrix in which the substance to be analyzed is contained, and improve specificity and selectivity in detection of the substance to be analyzed.
JP 2010-531995 A sets the size and shape of a nanofeature and the distance between nanofeatures such that an excitation frequency ω, a planar mode ωspp, and a localized surface plasmon mode ωLSP are equal, thereby exciting both the planar mode ωspp and the localized surface Plasmon mode ωLSP. Thus, the planar mode and the localized surface plasmon mode constructively interfere with each other to generate an electromagnetic wave having an electric field that is greater than either the enhanced electric field due to the localized surface plasmon mode or the planar mode, individually.
There is a disclosed method of increasing the enhanced factor of surface enhanced Raman scattering by arranging metal nanoparticles in the tetragonal lattice in Yizhuo Chu, Mohamad G. Banaee, and Kenneth B. Crozier, “Double-Resonance Plasmon Substrates for Surface-Enhanced Raman Scattering with Enhancement at Excitation and Stokes Frequencies”, ACS Nano, Vol. 4, No. 5, 2804-2810, 2010. According to the method, the distance between metal nanoparticles is appropriately set, whereby the electric field of laser light that excites surface enhanced Raman scattering is increased by plasmon resonance due to a grating effect; and the metal nanoparticles are provided such that the wavelength region of localized surface plasmon resonance by the metal nanoparticles themselves is matched to the position of the wavelength region of the generated Raman scattering, whereby the surface enhanced Raman scattering is very strongly enhanced.